The optical fiber is generally classified into a loose tube optical cable and a ribbon slot optical cable depending on the structure of the optical cable core. Among them, the loose tube optical cable is configured so that a plurality of optical fiber units in which the required number of optical fibers are mounted in a plastic tube together with jelly compound (hereinafter, referred to as ‘loose tube optical fiber unit’) are stranded around a tensile strength member positioned at the center of the cable. At this time, a plurality of the loose tube optical fiber units are stranded around the tensile strength member in a helical or an SZ strand in order to minimize the stress caused to the optical fiber by the bending of the optical cable when the optical cable is installed or taken up around a drum.
More specifically, referring to FIG. 1, the conventional loose tube optical cable 10 includes a tensile strength member 20 for minimizing various stresses exerted to the optical cable 10 when the optical cable 10 is taken up around a drum or installed in or out of a building, a plurality of loose tube optical fiber units 30 longitudinally stranded by a helical or an SZ method around the tensile member 20, a cable coating 50 for surrounding an aggregation of the tensile strength member 20 and the optical fiber units 30 and protecting an optical fiber 40 in the optical cable 10 from an external force when the cable is installed (e.g., side pressure or pulling), an external force after the installation of the cable (e.g., dropping of an article, compressive breakdown due to an article) and external circumstances (e.g., penetration of water), and a filler 60 for filling a space in the cable coating 50 except the loose tube optical fiber units 30.
However, in case there are required a smaller number of loose tube optical fiber units 30 in the loose tube optical cable 10 having the structure as shown in FIG. 1, the remained space in the cable coating 50 is replaced with inclusions in order to focus the stress on the tensile strength member 20 by keeping the optical cable 10 in its original form and minimize the stress of the optical fiber by keeping the helical or SZ strand of the loose tube optical fiber units 30 around the tensile strength member 20.
For example, FIG. 2 shows an optical cable of 1+6 structure in which 6 loose tube optical fiber units 30 should be stranded around one tensile strength member 20. However, if there are needed only two optical fiber units 30, the remained four loose tube optical fiber units are substituted with inclusions 70.
However, if the optical cable is manufactured by replacing the unnecessary loose tube optical fiber units 30 with the inclusions 70 as shown in FIG. 2 since the required number of the loose tube optical fiber units 30 is small in the loose tube optical cable 10, there is needed a process for maintaining the loose tube optical fiber units 30 and the inclusions 70 to be helically or SZ twisted around the tensile strength member 20. In addition, since the diameter and weight of the optical cable are not reduced due to the inclusions, there are increased the costs for manufacturing, carrying and installing the optical cable.